# 99 Aquarii

Observation data Constellation Epoch J2000      Equinox J2000 Location of 99 Aquarii (circled) Aquarius 23h 26m 02.78566s[1] –20° 38′ 31.251″[1] 4.37[2] K4 III[3] +1.815[2] +1.431[2] Suspected[4] Radial velocity (Rv) +15.7[5] km/s Proper motion (μ) RA: –50.72[1] mas/yr Dec.: –64.22[1] mas/yr Parallax (π) 11.51 ± 0.21[1] mas Distance 283 ± 5 ly (87 ± 2 pc) Radius 33[6] R☉ Surface gravity (log g) 1.66[7] cgs Temperature 3980[7] K Metallicity [Fe/H] –0.20[7] dex BD–21 6420, HD 220704, HIP 115669, HR 8906, NSV 14554, SAO 191900.[8] SIMBAD data

99 Aquarii (abbreviated 99 Aqr) is a star in the equatorial constellation of Aquarius. 99 Aquarii is the Flamsteed designation, although it also bears the Bayer designation b2 Aquarii. It is visible to the naked eye with an apparent visual magnitude of 4.38;[2] according to the Bortle Dark-Sky Scale this is bright enough to be seen even from city skies under ideal viewing conditions. Based upon parallax measurements, the distance to this star is around 283 light-years (87 parsecs).[1]

This is a giant star with a stellar classification of K4 III.[3] It is a suspected variable star that apparently ranges in magnitude between 4.35 and 4.45.[4] The measured angular diameter of this star is 3.55 ± 0.21 mas.[9] At the estimated distance of Delta Ophiuchi,[1] this yields a physical size of about 33 times the radius of the Sun.[6] The outer atmosphere has an effective temperature of 3980 K,[7] giving it the orange-hued glow of a cool, K-type star.[10]

This star was a candidate member of the Ursa Major Moving Group based on the work of American astronomer Nancy Roman, but this membership is now in question.[11]

## References

1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society, 172: 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667.
3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
4. ^ a b Samus, N. N.; et al. (March 2012), "NSV 14554", General Catalog of Variable Stars, retrieved 2012-07-12.
5. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1.. The radius (R*) is given by:
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(87\cdot 3.55\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 66\cdot R_{\bigodot }\end{aligned}}}
7. ^ a b c d McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
8. ^ "99 Aqr -- Variable Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-11.
9. ^ Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
10. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16.
11. ^ Chupina, N. V.; Reva, V. G.; Vereshchagin, S. V. (June 2006), "Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars", Astronomy and Astrophysics, 451 (3): 909–916, Bibcode:2006A&A...451..909C, doi:10.1051/0004-6361:20054009. See table 7.